Halogenated hydrocarbons, which may also be referred to as halocarbons, are important industrial chemicals and are produced in large quantities for various purposes. The chlorocarbons are collectively the most important halocarbons in industry and commerce but other halocarbons, especially the fluorohalocarbon refrigerants widely sold under "Freon" trademark are also important products. Examples of common halocarbons include methyl chloride, methylene chloride, chloroform, carbon tetrachloride, methyl bromide, methyl iodide, ethyl chloride, the dichloroethanes: 1,1-dichloroethane (ethylidene dichloride) and 1,2-dichloroethane (dichloroethylene), trichloroethylene, tetrachloroethylene, allyl chloride. These and other chlorocarbons are described in Kirk-Othmer, Encyclopedia of Chemical Technology, Third Edition, John Wiley & Sons, New York 1979, Vol. 5, 668-848, to which reference is made for details of these materials, their preparation and their uses. The brominated hydrocarbons, fluorinated hydrocarbons and iodo-hydrocarbons are described respectively, in Kirk-Othmer, op cit, Vol. 4, 243-263; Vol. 10 829-925 and Vol. 11, 1-81; and Vol. 13, 667-671, to which reference is made for details of these compounds, their preparation and uses.
Halocarbons are produced by a variety of processes which vary according to the convenience, cost and availability of suitable starting materials. Methyl chloride, for example, may be made by the direct chlorination of methane or by the reaction of hydrogen chloride and methanol; the other chloromethanes may also be made by direct chlorination of methane, as described in Kirk-Othmer, op cit. The chloroethanes may be produced by the hydrochlorination of ethylene, dhlorination of ethane and other processes described in Kirk-Othmer, ibid. Other halocarbons may be produced by various processes, as described in Kirk-Othmer, ibid.
The preparative procedures which use the fully saturated hydrocarbons such as methane as a starting material normally require the halogen to be used in its most active form, e.g., chlorine, rather than in the form of a possibly more convenient and safe halogenating agent because the fully saturated hydrocarbons are less active than their unsaturated or substituted derivatives such as methanol or ethylene. The use of the halogen itself may, however, be undesirable because it is unselective in its reaction with the hydrocarbon, producing a range of halogenated products from the mono-substituted to the perhalo compound. It would therefore be desirable to find a way of improving the selectivity of the halogenation reaction as well as developing a halogenation procedure which is capable of halogenating the saturated hydrocarbons, especially methane, directly using convenient and safe halogenating agents.